Istanbul, Turkey — At an emergency summit today, NATO and Turkey denounced Syria's shooting down of a Turkish military jet four days ago but sought to calm fears of a broader escalation between the neighbors.

Syria's shooting down of the jet was a deliberate and "heinous act" that has "changed" the rules of engagement for Turkish armed forces, Turkey's Prime Minister Recep Tayyip Erdogan told parliament today. Any Syrian military approach along their shared border will now be treated as a "threat" and a military target.

At a time when Turkey is hosting political and armed opponents of Syrian President Bashar al-Assad, Mr. Erdogan made clear that Turkey's response was deliberate and calculated but warned that that should not be taken as a "sign of weakness."

Likewise, NATO Secretary General Anders Fogh Rasmussen dialed back chances of a forceful response as the alliance met at Turkey's request in Brussels. Still, he said that downing the aging F-4 Phantom plane was a "completely unacceptable act."

Turkey and its NATO allies, despite talking tough, want to avoid getting entangled in Syria, where an uprising and insurgency continue for a fifteenth month. According to UN sources, as many as 14,000 have died so far. The conflict has taken on the flavor of a regional tug-of-war, with Syria and its Russian, Iranian, and Hezbollah allies on one side, pitted against Turkey and its US and European allies, which want to see Mr. Assad toppled.

"The government of Turkey has absolutely zero wish to be dragged into anything in Syria; they can see it's a complete mess," says Hugh Pope, a veteran Turkey analyst with the International Crisis Group.

"The only way Turkey will ever get involved in anything there is with complete international cover," says Mr. Pope. "They're going to NATO, they're going to international fora. It's all about [Turkey] being seen to do the right thing, it's not about hatching dark plots in the night with cruise missiles and taking things out [in revenge]."

Casus belli?

Erdogan said that Turkey was a brotherly, reliable nation, but that its "rage is very severe and intense" when warranted – a line that prompted chanting from Turkish parliamentarians.

Erdogan admitted that the Turkish jet had briefly been inside Syrian airspace, but insisted it was back in international air space by the time it was fired upon. He accused Syria of shooting down a clearly marked unarmed jet on a "training and test flight," without warning. "A short-term border violation can never be a pretext for an attack," he said.

Typical protocol required Syria to send out radio warnings first, and then scramble its own aircraft to warn the intruder, says Metehan Demir, a former military correspondent with close ties to the Turkish armed forces. "If those measures do not give a result, the last step is firing," he says.

Turkey claims Syria used a longer-range missile, which would make it more plausible that the jet was shot down outside Syrian territory. But the Syrians claim they used shorter-range anti-aircraft guns and say the Turkish jet was flying very low and well within their territorial waters, which they declared "sacred."

Turkey claims a second recovery jet which appeared shortly afterward was also shot at by the Syrians, adding to some reports in the Turkish press that Damascus "should pay."

"This shooting down of a Turkish plane will not be a casus belli, but Syria, one way or another, finally, ultimately, will pay the bill," says Mr. Demir, now the Ankara bureau chief for the mass circulation Hurriyet newspaper. "But how? Time will show us."

Erdogan called the Assad regime "cruel," and sought to justify his previous personal warmth with Syria's leader – before the uprising began, when they referred to each other as "brother" and close friends.

More recently, Erdogan said he recognized that the Syrians were "not telling the truth" about departing from the methods of Assad's father, Hafez, who as leader killed 30,000 people – Erdogan's number, though estimates vary – in the crackdown on the city of Hama in 1982. The younger Assad's regime, he said, was now maintaining the father's "hostile attitude to Turkey."

"The Syrian administration is not a legitimate administration anymore, and that we can see clearly," Erdogan told members of parliament. "Children, elderly, women, innocent people, civilians, were killed in a relentless manner by this tyranny."

Assad cornered 'like a cat'

Tensions have been high along the border for more than a year, with Turkey hosting defecting Syrian military officers who have formed the Free Syrian Army (FSA). Another general, two colonels, and some 30 other soldiers crossed into Turkey on Sunday night with their families.

Past incidents have involved Syrian assault rifle shooting toward camps in Turkey, where more than 32,000 Syrian refugees are being housed.

Syria says it is fighting "armed terrorists" and will stamp them out with force. Heavy shelling in recent months, especially in opposition strongholds like Homs, have turned apartment blocks to rubble, and created waves of homeless Syrians inside the country.

Syria has made clear that Turkey's actions are provocative. The New York Times reported last week that CIA operatives in recent weeks had begun helping funnel light weapons and other gear, paid for by Qatar, Saudi Arabia, and Turkey, to the FSA and opposition groups.

"Low intensity clashes between the two sides [may happen], but I don't think it will go to war," says Demir. "Some people accuse the Erdogan government of cornering Assad too much.... Like a cat, if it is cornered too much, finally it attacks you, it doesn't [care] if you are strong or not ... it reacts."

Turkey's counter-reaction will determine the scale of escalation. While Erdogan said there would be "zero tolerance" of any future Syrian transgression, he did not lay out a series of measures against Syria today, as widely expected.

"Even a punitive retaliation [against] the offending radar base ... may escalate already tense relations in the region to a completely new level," Abdullah Bozkurt wrote in a commentary in Today's Zaman newspaper. "Turkey may be venturing into dangerous and uncharted territory here."

Mehmet Seyfettin Erol, the head of the International Strategic and Security Research Center, told the newspaper that a broader conflict was under way, which pitted Syria – as the "resistance front" for the policies of Russia, Iran, China, and Iraq – against Turkey and its Western allies.

"By shooting down the Turkish plane, these countries wanted to give a message to the international community that they would protect this front at all costs, including a war," Mr. Erol said. "The incident is an open challenge from the Syrian regime. Turkey was not prepared for this challenge."